Planet around Alpha Centauri - lets talk about it

Inspired by the thread by Romulan spy I wanted to talk about this topic. So they believe they have found a planet in our nearest neighbor system but that seems to be about all they can tell at the moment. My question, what will it take to determine it's status?

Can a "class M" planet be viable in a stars system with 3 stars? If so, what leaps in technology will it take to get a good image of it? Can we make a some kind of spectral analysis to tell if it's really hot or large or what not. We'll want details.

I understand apparently it's so close it would be like writing a paragraph on the head of a pin, putting it right up to your eye and saying now read it. Just not doable. To me a little counter intuitive but who can argue with physics?! What do we need to develop in order to do it?

Just FYI, Alpha Centauri A and B are fairly widely spaced, with the closest approach of B to A being about the distance of Uranus to the Sun, so planets at Earthlike distances from either could possibly be perfectly stable climatically.

Proxima Centauri is a 20th of a light year from the main pair, ergo no real influence.

Well, let's have some fun with a calculator and see what it would take to image a planet at that distance.

The distance to Alpha Centauri is 4.367 light years and a light year is 9.460528e12 kilometers, so the distance is 4.131e13 km. The resolution of a telescope (separating two stars by eye) is res = 4.56 arc seconds / diameter in inches. Trigonometry says the sin of one arc-second is 4.848e-6 times the distance, so an arc-second resolution can distinguish two objects that are 200 million kilometers apart at the distance of alpha centauri.

The Hubble has a resolution of about 0.05 arc seconds, so it can resolve to about 10 million kilometers at that distance. (The Earth is 12,742 km in diameter. Dawe's limit (the 4.46/d" formula) for telescope resolution says the Hubble's 94.5 inch diameter aperture should resolve to about 0.0483 arc seconds.)

Supposing we wanted a telescope that could distinguish between two planets and Earth-diameter apart at the distance of Alpha Centauri, we'd need a telescope that could resolve down to 12,742 km or 127.42 km, which by trigonometry would be 1.767e-8 arc-seconds and require an aperature of 4,000 miles. To resolve an Earth-size planet into an image size of 120x120 useful pixels would take a 480,000-mile diameter telescope, which if centered on the Earth would span out to the orbit of the moon. We couldn't build a single mirror that vast, but all we need are dozens or hundreds of small mirrors in orbit whose angle can be controlled so their surface is aligned to within an 1/8th wavelength of light. We could probably do that in the not so distant future (relative to launching anything to Alpha Centauri).

Scaling such a set of satellites up isn't all that hard, so I'd imagine that we could be producing useful images of nearby planets from our own solar system long before we could construct a ship to visit them.

Proxima Centauri is a 20th of a light year from the main pair, ergo no real influence.

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Well, not exactly -- it could have a positive influence. In our system, the Sun's heat burned off all the water in the inner system, and it was bombardment by comets from further out that restored water to the Earth. But Alpha Centauri A & B's respective gravity would've scattered any outer planets or comets (plus you've got the heat of two stars to evaporate volatiles), so if there were just the two stars, any planets around them might be bone-dry. However, assuming that Proxima Centauri actually orbits A & B rather than being an independent star that's just passing by (there's still some doubt about that), then its gravity could've sent comets from the system's Oort cloud inward to bombard the planets, so they could have water after all.

Although the flipside is that they'd still be getting bombarded with comets periodically, which might hurt the chances of higher life or civilization evolving there.

Venusians try to push their claim of "equal size" on all the forums, but despite their pleadings, Venus remains slightly smaller and far less significant than Earth. The little CO2 sucking thermophiles are eaten with envy and I generally ignore the way they try to insert themselves into any conversation, but at least they're not as bad as the martians (which I still refuse to spell with a capital 'M' because of a dustup with a certain someone who tried to kill one of my bunnies and conquer my planet).

In our system, the Sun's heat burned off all the water in the inner system, and it was bombardment by comets from further out that restored water to the Earth.

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Total speculation. There are many hypotheses of Solar system formation, and most have serious problems. The nebular hypothesis is especially weak, with conservation of angular momentum one of its bigger problems. And since several comet missions have observed comets close up as bone-dry rocks with little or no volatiles, the idea of comets giving Earth its oceans (or using comets to Terraform Mars) is untenable.

And since several comet missions have observed comets close up as bone-dry rocks with little or no volatiles, the idea of comets giving Earth its oceans (or using comets to Terraform Mars) is untenable.

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Well, that's categorically false. Of course some comets would've exhausted their volatiles after enough passes near the Sun evaporated them all, but comet missions and other astronomical observations have confirmed the presence of water and volatiles on comets. In fact, this was just in the news. Other findings of water and volatiles in comets:

True, there is some legitimate debate about whether comets were the primary source of Earth's water -- some findings suggest it may have been meteorites from the inner portions of the system instead. But nobody is claiming that comets are bone-dry -- except for one crackpot page I found with lots of exclamation points and misspelled rantings about scientist conspiracies and extended tracts on politics and philosophy.

At the rate these discoveries are being made for exo-planets, and Earth-like planets, and habitable zone earth-like planets, and closest Earth-like planets...

I feel like we'd finally send off an interstellar ship or probe on a 100 year journey to an exo-planet and six months later

OH!!!

We just found the first Class M exo-planet eight light years in the other direction.

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What's more likely to happen is if we sent a probe or ship on a 100 year journey to reach the Earth like planet, when they get there they realize the team we sent 50 years later with better technology beat them there.

But nobody is claiming that comets are bone-dry -- except for one crackpot page I found with lots of exclamation points and misspelled rantings about scientist conspiracies and extended tracts on politics and philosophy.

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Then you're not looking very hard. There are plenty of sites with no misspellings, exclamation points, rants, or conspiracy theories. But if a site does not agree with mainstream astrophysics, you might still call them crackpot.

The point is, most people have no idea how tenuous astronomical models are, yet they are always presented as hard fact.

But if a site does not agree with mainstream astrophysics, you might still call them crackpot.

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Hey, no need to get personal.

The point is, most people have no idea how tenuous astronomical models are, yet they are always presented as hard fact.

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Now, that's simply not true. Science never claims to be the absolute revealed truth. The whole process of science is built around testing and questioning hypotheses -- basing conclusions on the evidence, and changing theories to fit new evidence. Of course there's always room for doubt and re-evaluation in light of new evidence. But what you're doing is ignoring hard evidence we already have that proves there are water and other volatiles on comets.

Thank you everyone for this discussion, very interesting. So the planet is most likely a hot lava like planet, ouch and a pity as it is the closest. I don't think a robotic mission to any other planet we find would be doable, just to far, 8 light years might as well be 50,000. Loved all the extended reading offered here so again, thanks.

Since we don't currently have a way to view the planet, should we consider sending a message to the system? I know we've been transmitting radio and TV signals for a long time, but if there is an inhabited planet there, a powerful signal, directed at specific system may get their attention. That is if we haven't ruled out other planets orbiting either star.

Alpha Centauri Bb is the only planet we've detected in that system so far, because it's the easiest one to detect using our methods. As I believe I remarked above, we don't yet have the technology to detect an Earth-sized planet in the habitable zone of either star. So it's way too early to rule out other planets in the Alpha Centauri system. It'll probably take a few more years before we have the means to see what else is there.